Frequent recombination contributes significantly to the diversity of the HIV-1 population. We have studied multiple aspects of HIV-1 recombination. We have studied the recombination potential of subtype A HIV-1 using strains that are circulating in Russia, and we found that recombination occurs frequently and can easily assort mutation to generate variants resistant to multiple antivirals. We have also studied how host restriction factors APOBEC3G and APOBEC3F affect viral replication, and whether hypermutations induced by these restriction factors play a role in viral evolution. Additionally, we have assisted in the construction of replication-dependent vectors that can be used to monitor cell-to-cell infection. These studies will reveal insights into the replication mechanisms of HIV-1. [Corresponds to Hu Project 1 in the October 2011 site visit report of the HIV Drug Resistance Program, renamed the HIV Dynamics and Replication Program in 2015]